1. Field of the Invention
The invention relates to a munition for use in marine environment. More particularly the invention relates to an explosively formed projectile (EFP). The invention also relates to a method of increasing range and velocity of an explosively formed projectile in water.
2. Discussion of the Related Art
An explosively formed projectile (EFP) is a type of munition that combines an explosive charge with a projectile forming work piece. The work piece is shaped by explosive forging into an elongated, solid projectile during explosive detonation. Besides an explosively formed projectile (EFP), other explosively formed projectiles include the shaped charge (SC) and the High Explosive Anti-Tank (HEAT) munition.
The essential element of a shaped charge (SC) is a liner that on firing forms an elongated hyper-velocity metal jet that is projected toward an armored target. The generally cone-shaped liner has a relatively small diameter and produces deep, relatively small diameter penetration of the target. Continuity of the elongated shaped charge (SC) jet breaks up with extended travel distance to the target. Break-up alters the shape of the jet; most significantly at target impact. Therefore it is necessary to reduce standoff distance to a length that allows an effective continuous jet to impact the target. In military applications, the shaped charge (SC) is often combined with a rocket to form a rocket propelled grenade (RPG) assembly. In a rocket propelled grenade (RPG) the rocket carries the shaped charge explosive munition to the target. The explosive charge is ignited on contact with the target and the projectile jet is formed inside the shaped munition housing. This arrangement results in a very short penetrator jet travel distance before impacting the target. Shaped charges (SC) have high impact velocities of about 3 to 4 kilometers/second.
A High Explosive Anti-Tank (HEAT) munition also relies on a cone-shaped liner that is explosively formed into a narrow, relatively long jet penetrator. Relatively more time is required for the formation of the penetrator jet. The shape of the cone liner and configuration of the explosive charge are adjusted for desired results. The HEAT munition requires sufficient standoff distance from the target to form before target impact. Therefore, it is necessary to increase standoff distance to a length that allows an effective jet to impact the target. A delivery mechanism ignites the explosive charge at a required distance from the target. A HEAT munition is usually contained in an anti-tank shell or missile. The velocity of the shell or missile and distance from the target are included in the time of ignition calculation of the delivery mechanism. HEAT penetrators have high impact velocities of about 10 to 15 kilometers/second.
An explosively formed projectile (EFP) is explosively forged from a dish-shaped metal work piece into a single, compact, relatively massive penetrator. The EFP is accelerated to a velocity of 1 to 3 kilometers/second which is less than the velocity of a shaped charge (SC) or High Explosive Anti-Tank (HEAT) projectile. The essential explosively formed projectile (EFP) munition includes a generally cylindrically-shaped case containing an explosive charge and a dish-shaped metal liner. The dished liner is positioned at a forward end of the case and an explosive charge initiator is positioned aft. EFP warheads are designed to produce a compact, high velocity penetrator. After detonation, the charge produces an explosive blast pressure that accelerates the liner and simultaneously reshapes the shallow dish-shaped liner by rearward folding into a compact, slug-shaped projectile. The compact slug is fundamentally distinguished from an elongated shaped charge (SC) jet or elongated HEAT jet. The EFP slug is able to traverse a relatively longer standoff distance before impacting the target, and deliver a relatively large diameter high mass projectile. The destructive potential of a penetrator is quantified by kinetic energy at impact. Kinetic energy is quantified as the product of the projectile mass and the square of the impact velocity. The EFP has an impact velocity in air in the range of about 1 to about 3 kilometers/second.
Explosively formed projectile (EFP) munitions have been developed and modified over time to facilitate penetration of armor targets. The several parameters in the munition configuration have been adjusted to achieve penetration of improved generations of ballistic armors. EFP modification investigations have been directed to penetrating land and air targets but not to targets in water. It has been thought that the formation of a slug projectile would be inhibited in a water environment. More specifically, water would cause a drag on the projectile and full potential velocities could not be achieved. Explosively formed projectiles (EFP) have been investigated with the objective of overcoming the adverse effects of water. However, the explosively formed projectile (EFP) has not achieved its potential in marine use.
There is a need in the naval ordnance arts for an explosively formed projectile (EFP) munition that performs effectively in water.